2004 MG ZR central locking

my central locking is making a grinding noise when the doors are locked with the remote the boot lock was not working too so i replaced the catch and the plastic locking unit which worked when the boot was open but on closing the boot the n locking with the remote the boot will not lock i then orened the boot pressing the fob the locking mech on the unit retratced so i placed a screw driverl locking the latch and pressed the remote the unit failed to work any help as i dont want to replace parts if i dont need to thanks vince